Method and apparatus for dispersing coagulant into a water stream

ABSTRACT

A chemical additive is thoroughly and almost instantaneously mixed with huge quantities of water flowing through a large pipe or flume by dividing the additive into equal smaller streams, and feeding the chemical additive streams separately but at equal rates to a plurality of points equally distributed along the cross-section of the flow and vigorously churning the combined stream at a point just downstream from this feeding of the chemical solution. The churning is preferably by opposed propellers. Two propellers on a shaft, or on each of a plurality of shafts, each impel the water in the direction toward the other. As the water leaves the churn zone, it passes between stilling vanes parallel to the general direction of flow. Flow through the unit is preferably sufficiently constricted to increase flow turbulence and to prevent bypassing of water not fully blended, but the system nevertheless avoids excessive head loss.

United States Patent Walker 51 May 30, 1972 {72] Inventor: James DonaldWalker, Aurora, Ill.

[73] Assignee: Chicago Bridge & Iron Company [22] Filed: Nov. 24, 1969[21] Appl. No.: 879,410

[52] U.S. C1 ..2l0/49, 210/206, 259/7 [51] Int. Cl ..B0ld 21/01 [58]Field ofSearch... ....259/4, 7; 210/42, 59, 49, 198, 210/206; 137/1 [56]References Cited UNITED STATES PATENTS 1,362,611 12/1920 Ellms ..2l0/493,470,091 9/1969 Budd et a1 ..210/199 X Primary ExaminerMichael RogersAttorneyDarbo, Robertson 8:. Vandenburgh [5 7] ABSTRACT A chemicaladditive is thoroughly and almost instantaneously mixed with hugequantities of water flowing through a large pipe or flume by dividingthe additive into equal smaller streams, and feeding the chemicaladditive streams separately but at equal rates to a plurality of pointsequally distributed along the cross-section of the flow and vigorouslychurning the combined stream at a point just downstream from thisfeeding of the chemical solution. The churning is preferably by 0pposedpropellers. Two propellers on a shaft, or on each of a plurality ofshafts, each impel the water in the direction toward the other. As thewater leaves the churn zone, it passes between stilling vanes parallelto the general direction of flow. Flow through the unit is preferablysufficiently constricted to increase flow turbulence and to preventbypassing of water not fully blended, but the system nevertheless avoidsexcessive head loss.

9 Claims, 9 Drawing Figures Patented May 30, 1972 Sheets-Sheet 1INVENTOR JAMES DONALD WALKER y 9%,MX3MM Attorneys Patented May 30, 19722 Sheets-Sheet 2 lNVENTOf? JAMES DONALD WALKER METHOD AND APPARATUS FORDISPERSING COAGULAN'I INTO A WATER STREAM BACKGROUND OF THE INVENTIONThis invention provides an advance in the art of instantaneouslydispersing additives throughout huge quantities of water flowing througha pipe or flume. It can be used, for example, to disperse coagulantsolutions and thus, it is particularly useful in preparing water forfiltration inasmuch as unfilterable colloids are occluded within large,insoluble, inert coagulant aggregates which either settle out or arefilterable. In recent years it has been reported that variations indesign or operation of equipment for mixing treatment chemicals in watercause a greater effect on filtered water quality than do variables inthe final filtration process itself. Moreover, it has become appreciatedthat in order to achieve the theoretical ultimate in efficiency oreffectiveness of a coagulant such as conventional aluminum or ironcoagulants, the dispersal of the coagulant chemical solution throughoutthe water to be treated must occur within a very short, critical timeperiod, that is virtually instantly. According to the presentunderstanding of the science of water treatment the dissolved coagulantis converted to a relatively inert, coagulated condition almostinstantaneously upon being dispersed; and, colloidal particles which arenot reached by the coagulant during the instant of dispersion of thecoagulant throughout the huge amount of raw water may not besubsequently picked up by the coagulant in the flocculation zone whereonly aggregate growth takes place. Frequently, in some plant operations,some colloidal particles remain uncoagulated because of less thanadequate dispersion of the coagulant chemical solution at the instant ofdispersion of that solution into the raw water. In some plantoperations, due to inefficient dispersion of the coagulant solution,excessive quantities of coagulant are rou-' tinely added in an oftentimes futile attempt to overcome the lack of dispersion efficiency. Withwater quality standards becoming more and more stringent, and the costof treatment chemicals rising, the efiiciency and fidelity of thecoagulant blending phase is of prime importance in quality waterproduction.

Numerous blending methods and apparatus have been suggested fordispersing coagulants into raw water in preparation of the water forfiltration or other clarification. However, in addition to thedifficulty encountered in achieving immediate uniform distribution ofcoagulant throughout the raw water stream, the equipment and methodsavailable prior to this invention incurred large head loss, generallyspeaking. Early efforts utilizing a series of baffles in a channelproved very inefficient for rapid blending in spite of having high headloss. This method was followed by mechanical rapid mixing units,installed in basins with two to five minute retention periods. Theseunits were presumed to be efficient and have been popular for manyyears. However, in fact, these basins failed to achieve completeblending of the coagulant with raw water within the critical timeperiod. For example, the so called rapid-mix basins were too large toblend instantaneously, under through-put conditions, the coagulant feedwith every portion of the water. They were found to be prone to drasticshort circuiting," some of the water finding a path from inlet to outletthat escaped the mixing action.

One of the objects of this invention is to provide a method and devicefor almost instantaneously dispersing coagulants through every portionof large quantities of in-stream water, with a minimum head loss. It isan object of this invention to provide a device for constantly blendinga coagulant throughout each increment of flowing raw water inmilliseconds.

SUMMARY OF THE INVENTION Minuscule quantities of additive solution arealmost instantaneously distributed throughout every incremental portionof a huge water stream flowing through a large pipe or flume by dividingthe additive into a plurality of carefully metered smaller streams,passing the individual added streams into the larger water stream at aplurality of points in the cross-section of the large stream, in a zonein which the entire water stream is subjected to turbulence as it passesthe point of injection.

DESIGNATION OF THE FIGURES FIG. 1 is a schematic elevational viewillustrating a utilization of the improvement of this invention in awater treatment system.

FIG. 2 is an enlarged partially cross-sectional elevational view.

FIG. 3 is a perspective view of a disc-vane assembly used in theembodiment of FIGS. 1 and 2.

FIG. 4 is an elevational view taken approximately along the line 4-4 ofFIG. 2.

FIGS. 5 through 8 are views taken approximately as in FIG. 4, andillustrate alternative designs for vane-systems which can be used inaccordance with this invention.

FIG. 9 is a view approximately as in FIG. 3 illustrating the use of aplurality of agitators.

DESCRIPTION OF PREFERRED EMBODIMENTS Mixing station 15, improved inaccordance with this invention, is incorporated into raw water feed line17. Mixing station efiluent proceeds to a clarifier, 19,diagrammatically shown, which includes relatively wide diameter basin21, overflow troughs 23 and gentle-agitation section 25. From theclarifier overflow 23, the water proceeds to filtration stations (notshown) in other conventional processing stations.

Raw water line, 17, includes coupling section 27 pipe 28 of mixingstation 15, and clarifier input line 29. Pipe 28 of mixing station 15 issecured to sections 27, and 29 by conventional butting joint flanges 31,secured by customary nuts and bolts 33. However, interposed betweenopposing flanges 31 at both upstream joint 35, and downstream joint 37,are baffle discs 40, each having peripheral section 42, in-line bafflesection 44 and spaced openings 46 in peripheral section 42 for passageof bolts therethrough. In the embodiments illustrated in FIGS. 2, 3, 4and 7, vertical vane 50 and horizontal vanes 52 are secured to bafflesection 44 by welds 54. Horizontal vanes 52 are also secured to verticalvane 50 by welds 56. Vertical vanes 50 include extensions or projections60 extending from end 62 of vane 50 which is most distant from disc 40.Openings 65 are provided in vertical vanes 50 to permit passagetherethrough of additive secondary feedlines which will be described indetail hereinafter. In the illustrated embodiment two identicaldisc-vane assemblies 70 are utilized, one at upstream joint 35, withvanes 50, 52 extending downstream, the other at downstream joint 37 withits respective vanes 50, 52 extending upstream.

Additive Injection System Main additive feedline 75, for example, a lineconnected to a source of coagulant-chemical solution in a watertreatment plant, is connected to a plurality of valved flow meters 77.The flow through each flow meter 77 is accurately regulatable by itsrespective valve 79. Branch additive lines 81 pass from respective flowmeters 77 through access plate 83 to the interior of pipe 28. Accessplate 83 is sealed around secondary feedlines 81. Each of branchfeedlines 81 ends in a respective section 86 of the interior of pipe 28formed by vanes 50, 52, preferably discharging its stream of additivenear the centroid of the cross section of its respective section, asperhaps best seen in FIG. 4. Each 1: shown in sections 86 in FIGS. 5through 8 indicates the preferred approximate point of injection in eachof the illustrated configurations.

Sections 86 are defined as that fractional portion of thecross-sectioned area of the stream pipe or flume, represented by thetotal cross-sectional area divided by the number of branch additiveinjection points. In the preferred embodiment, each section 86 isbounded by physical walls or dividers, e.g., vanes 50, 52, though thepresence of the vanes is not absolutely essential. It is possible thatthe vanes can be omitted, provided that in some way, flow past, and inclose proximity to, each additive injection point is made a consistentpart of the whole, with sufficient equality between the flows to achievethe uniformity of distribution desired. It is important, however, thatthe chemical streams be injected at enough points distributed throughthe cross-section of flow, with an approach to equalizing of dosingrates, and with sufiicient agitation immediately upon injection, toachieve instantaneous mixing throughout the entire mainstream.

Flow meters 27 are preferably of the conventional type in which anindicator rises in a tapered tube, its height increasing as the flowincreases. With the indicators all at the same level, the equality offlow usually desired is achieved. If any constructional features orother factors might induce less flow in some sections 86, than others,an operator can experiment and see if the rate of injection to thatsection can be reduced without impairing the ultimate results. Theequality of dosing rate desired is that which will amount to the samepercentage of coagulant to the water flowing through each section 86.

Power Mixer Power mixer, generally 96, includes motor means 93,transmission means such as pulley system 100, gear box 102, shaft 104,upper propeller 106, and lower propeller 108. Propellers 106, 108, arepitched to propel water in opposite directions, preferably toward eachother, as indicated in FIGS. 2 and 4. It is noted that extensions 60 ofvanes 50, parallel to the general direction of flow of liquid passingthrough pipe 28, are located axially with respect to the axis ofrotation of the impellers, and serve as rotation spoilers. Although theyact directly on the water approaching the impellers axially, they reducethe rotation of the entire body of water surrounding each shaft.

Alternative Constructions Disc-vane assembly 70 can be modified,depending on the size of pipe 28 and the quantity of water into whichthe additive is to be dispersed, to include a larger, or smaller, numberof sections 86. Each section would have a branch additive feedline 81.Thus, as illustrated in FIGS. 5 and 6 vanes 110 may be used in a varietyof angular spacings. In a relatively small pipe 28, one vane 50 willsuffice, as illustrated in FIG. 8. If shaft 40 should be horizontal, itwould also be horizontal. It is essential, in accordance with thisinvention, that a branch additive feedline 81 inject a proportionalportion of additive in each of the sections 86.

As illustrated in FIG. 9 a plurality of mixers 112 on shafts 114 may bepositioned along a plane perpendicular to the general direction of flowthrough pipe 28, and this arrangement is particularly preferred inembodiments in which pipe 28 is of relatively large diameter. Rotationspoilers 60 should be provided for each shaft, as close to the plane asconvenient. Separate pieces may be welded in place if no vane 110 isreasonably near the plane.

Operation Raw water, or other liquid through which a relatively smallquantity of additive is to be dispersed, passes through feedline 17 inthe direction indicated by the horizontal arrows of FIGS. 1 and 2.Upstream baffle 40 causes considerable turbulence immediately downstreamthereof in the region between upstream and downstream end of mixingstation 15. It and vanes following it also tend to ensure equal flowthrough the various sections 86. A main stream of additive, passingthrough main feedline 75 is split into'a plurality of branch streams, inthe embodiment of FIGS. 2 through 4, into four streams, and the relativequantity of additive liquid passing in each of the branch streams isoperator-controlled using conventional flow meters 77 such as rotametersto provide substantially equal secondary streams passing throughrespective branch additive lines 81. Thus, material passing throughlines 81 and being discharged into sections 86 are discharged into aviolently turbulent region within mixing station 15. When power mixer 96is in operation, fluid is drawn from outer zones of pipe 28 and driveninward, axially of shaft 40. This vigorous agitation complements themixing action of upstream baffle 40. At relatively low rates of flow,i.e., at rates of flow well below the design limit for the particularpipe 28, turbulence generated downstream of upstream bafile 40, isinsufficient for the desired quick and complete dispersal of additivethroughout the mass of liquid passing through each of sections 86.During these relatively low flows mixer 96 nevertheless providesvirtually instantaneous homogenization, i.e., homogeneous dispersion ofthe additive solution throughout the water passing through pipe 28.Thus, within a fraction of a second, perhaps even within a fewmicroseconds, depending on the rate of flow through feedline 17, theadditive solution is completely dispersed throughout each increment offluid passing through mixing station 15.

Additional additive feedlines 81 and stream sampling lines 93 may beadded through access plate 83 as suggested at the phantom lines in FIG.2. Lines 91, 93, however, terminate downstream of downstream bafile 40,and hence can be used for sampling, or can be used to discharge asupplementary additive, e.g., alkaline agents, solid carbon in a slurry,polyelectrolytes, etc. into the main stream outside of the mixingstation 15. Turbulence in the downstream region generated by downstreambaffle 40 continues the homogenization or thorough mixing of the streamwell past mixing station 15. Also, upstream line can be used to add phmodifiers, or other modifiers as required by the chemistry of theparticular raw water stream.

Reports on actual tests in water treatment plant indicate that using thepreferred embodiment illustrated in FIGS. 1 2, and 4 herein, the qualityof water passing from a final filter of a water treatment plant wasimproved by the use of the illustrated embodiment, even thoughsubstantially 20 percent less coagulant chemicals than before wererequired. Also, in the same test, head loss of less than 1 foot wasreportedly encountered through mixing station 15. This may be comparedto a mixing station of the prior art which had reportedly been tried atthis point, but not successfully used because its head loss wasprohibitive, about I2, feet.

The improved quality of the water with less coagulant appears to resultfrom the quick uniform dispersal of the coagulant. Samples taken atsample lines 93 during operation of the embodiment illustrated in FIGS.1, 2, and 4, showed the complete equalization of the concentration ineach section, of an additive added through branch lines 81. As indicatedabove, operation of mixing station 15, in accordance with thisinvention, at relatively low flows through pipe 28, i.e., at flows wellbelow the maximum design capacity, does not provide sufficientturbulence or churning within station 15 due to the action of upstreambaffle 40 alone. When mixing station 15 is operated under theserelatively low flow conditions, therefore, use of power mixer 96 isessential.

It should be noted that in the design and construction of municipalwater treatment plants, for example, it is considered good engineeringpractice to provide for substantial expansion of operating capacity forthe increases normally encountered in a foreseeable future. Thus it isconsidered good practice, by many engineers, to design and build a watertreatment plant capable of handling present requirements as relativelylow flow, and which is capable of handling a substantially increasedflow. Using the embodiment of this invention illustrated in FIGS. 1, 2,and 4 herein, power mixer 96 is preferably used in the early years ofoperation of the water treatment plant in which the flows are well belowdesign capacity. It should be noted however that as the flow throughpipe 28 approaches the design capacity, sufficient turbulence may existwithin section 28 of the illustrated embodiment to instantaneously andcompletely homogenize and mix additives throughout the stream, even withpower mixer 96 not in operation.

However, in general, it is preferred that power mixer 96 be operatedeven at relatively high rates of flow at which power mixer 96 might beunnecessary, to better assure complete, instantaneous dispersion ofcoagulant through the water to be treated. Nonetheless, an operatorwishing to economize even at some risk can stop power mixer 96 or, ifpractical, incremently diminish its speed, while mixing station iscarrying a full or heavy flow, and observe the quality of the waterleaving final filtration. This, of course, is the final and mostimportant test of the efficacy of the coagulant-mixing operation takingplace at station 15 and this, of course, is the best test by which anoperator of a specific unit, processing a specific raw water candetermine whether continued operation of power mixer 96 is required atany specific high flow condition. If the quality remains undiminished,it is apparent that the multipoint injection at a point of flow-inducedturbulence is a sufficient use of the present invention. However, evensuch an economical operator should test further to see if with the mixer96 in operation and see if the amount of coagulant can be reduced enoughto offset the cost of power for mixer 96.

Thus, in accordance with this invention, virtually instantaneous mixingof additive, for example, chemical coagulants in water treatment streamsis provided, with the result that decreased levels of additive have beenfound to be sufficient to provide improved water quality, and with theresult that head losses encountered using the invention are vastly andastoundingly less than the head loss encountered in using the prior artrapid mixers. To illustrate the use of the mixer of this invention,addition of coagulant chemicals to raw water has been discussed indetail. This invention is not limited to such use, however, and isgenerally useful wherever relatively small amounts of one liquid must bedispersed throughout a relatively large volume of a second liquid. Thisinvention is especially important when very quick dispersal is required,but represents an economy in the amount of mixing energy required, evenwhen speed is not important.

I claim:

1. Apparatus for dispersing coagulant solution into a raw water streamflowing through a conduit comprising:

means for dividing a stream of additive into a plurality of secondaryadditive streams;

means for regulating and measuring the flow in each of said secondaryadditive streams;

means for conveying and injecting each of said secondary additivestreams into said raw water stream each at a respective discharge pointin said raw water stream, said discharge points being spaced apartthroughout the raw water stream; and

annular constriction means located upstream of said discharge points forgenerating turbulence in said raw water stream, said discharge pointsbeing positioned in the zone of said turbulence.

2. An apparatus for instantaneously mixing a relatively small additivestream throughout a relatively large fluid stream comprising:

means for dividing the primary additive stream into a plurality ofsecondary additive streams;

means for regulating the flow in each of said secondary additivestreams;

means for measuring the rate of flow in each of said secondary additivestreams;

means for conveying and injecting each of said secondary additivestreams into said large fluid stream at respective injection points,said respective injection points being widely spaced apart from eachother;

constriction means extending into said large fluid stream whereby a zoneof turbulence is generated adjacent to and downstream of saidconstriction means, said injection points being positioned in said zoneof turbulence; and

power mixing means comprising a pair of propellers on a shaft, motormeans for rotating said shaft, said propellers being pitched to movefluid in said stream in opposite directions, said shaft being positionedperpendicular to the general direction of flow of the stream, saidmixing means being located downstream of, and adjacent to said injectionpoints.

3. An apparatus as in claim 2 in which the large stream is divided intoa plurality of substantially equal sections by a first set of vanesadjacent to and downstream of said constriction means, each of saidinjection points being positioned within a respective section,approximately at the centroid of its respective section.

4. An apparatus as in claim 3 including a second set of vanes dividingsaid stream into a plurality of sections, said set being fixed to thewall of the fluid stream conduit and being positioned adjacent to anddownstream of said power mixing means.

5. In a mixing station including means for mixing a stream of raw water,means for injecting a primary additive stream into the raw water stream,the improvement in which the mixing station includes:

a plurality of segments of pipe butted end to end and joined byexternally fastened opposing joint flanges;

an annular disc having an opening therethrough, and a planar portionsized for positioning between said opposing flanges and for providing anextending portion extending into the raw water stream;

means for splitting said primary additive stream into a plurality ofsecondary additive streams;

control means for measuring and controlling the flow rate through saidsecondary additive streams;

means for conveying and discharging said secondary additive streams intosaid raw water stream at a plurality of respective injection points;

a first set of vanes fixed to said extending portion and separating thelarge stream into a plurality of smaller streams therebetween, each ofsaid respective injection points being positioned in a respectivesection near the centroid thereof;

mixing means comprising a pair of propellers fixed to a shaft, means forrotating said shaft, said propellers being pitched to urge fluid in theconduit in opposite directions, said shaft being positionedsubstantially perpendicular to the direction of flow of the fluid, saidpropellers being positioned adjacent opposite walls of said conduit.

6. In a mixing station as in claim 5 which includes a second annulardisc having an opening therein, said second disc being positionedbetween the opposing joint flanges which are downstream with respect tosaid mixing station, said second annular disc having projecting portionsextending into the stream;

a second set of vanes for dividing said stream into a plurality ofsections, said second set being fixed to said projecting portions ofsaid second disc and extending upstream with respect to said seconddisc.

7. A method of achieving uniform and substantially instantaneousdispersion of a coagulant of a type most efficiently used bysubstantially instant dispersion, including the steps of:

flowing a large stream of liquid to be treated through a conduit; v

injecting a coagulant of said type, divided into several separatestreams of predetermined flow rations, into said large stream nearcentroids of cross-sectional sectors of the large stream havingcorresponding flow ratios; and

providing turbulence in the large stream for distributing the coagulantthrough it, said turbulence including turbulence of the cross-sectionalsectors of the large stream at positions to begin the mixing of thecoagulant therein substantially instantly upon injection of thecoagulant; and including a zone of vigorous turbulence with major flowinduced by propulsion means moving transversely throughout the largestream in a zone positioned to mix the coagulant throughout the largestream promptly after injection, with vigorous flow from at least onetransversely acting impeller passing through and intermixing a pluralityof sectors.

8. Apparatus for achieving uniform and substantially instantaneousdispersion of a coagulant including:

a conduit through which flows a large stream of liquid to be treated;

means for injecting a coagulant, divided into several separate streamsof predetermined flow ratios, into said large stream near centroids ofcross-sectional sectors of the large stream having corresponding flowratios; and

means for providing turbulence of the cross-sectional sectors of thelarge stream at positions to begin the mixing of the coagulant thereinsubstantially instantly upon injection of the coagulant;

said apparatus including propulsion means for providing vigorousturbulence in a zone positioned to mix the coagulant throughout thelarge stream promptly after in jection by causing flow transverselythroughout the large stream, with vigorous flow from at least onetransversely acting impeller passing through and intermixing a pluralityof said sectors. 9. A method of achieving uniform and substantiallyinstantaneous dispersion of a coagulant of a type most efficiently usedby substantially instant thorough dispersion, including the steps of:

flowing a large stream of liquid to be treated through a conduit;

injecting a coagulant of said type, divided into several separatestreams of predetermined flow ratios, into said large stream nearcentroids of cross-sectional sectors of the large stream havingcorresponding flow ratios; and

providing turbulence in the large stream for distributing the coagulantthrough it, said turbulence including turbulence of the cross-sectionalsectors of the large stream at positions to begin the mixing of thecoagulant therein substantially instantly upon injection of thecoagulant; and including not later than immediately after injection azone of vigorous turbulence with flow moving the coagulant at leastthroughout substantially the entire cross section of each sector of thestream by movements transversely of the main direction of stream flowand transversely of each other to mix the coagulant with good uniformitythroughout the large stream promptly after injection.

2. An apparatus for instantaneously mixing a relatively small additivestream throughout a relatively large fluid stream comprising: means fordividing the primary additive stream into a plurality of secondaryadditive streams; means for regulating the flow in each of saidsecondary additive streams; means for measuring the rate of flow in eachof said secondary additive streams; means for conveying and injectingeach of said secondary additive streams into said large fluid stream atrespective injection points, said respective injection points beingwidely spaced apart from each other; constriction means extending intosaid large fluid stream whereby a zone of turbulence is generatedadjacent to and downstream of said constriction means, said injectionpoints being positioned in said zone of turbulence; and power mixingmeans comprising a pair of propellers on a shaft, motor means forrotating said shaft, said propellers being pitched to move fluid in saidstream in opposite directions, said shaft being positioned perpendicularto the general direction of flow of the stream, said mixing means beinglocated downstream of, and adjacent to said injection points.
 3. Anapparatus as in claim 2 in which the large stream is divided into aplurality of substantially equal sections by a first set of vanesadjacent to and downstream of said constriction means, each of saidinjection points being positioned within a respective section,approximately at the centroid of its respective section.
 4. An apparatusas in claim 3 including a second set of vanes dividing said stream intoa plurality of sections, said set being fixed to the wall of the fluidstream conduit and being positioned adjacent to and downstream of saidpower mixing means.
 5. In a mixing station including means for mixing astream of raw water, means for injecting a primary additive stream intothe raw water stream, the improvement in which the mixing stationincludes: a plurality of segments of pipe butted end to end and joinedby externally fastened opposing joint flanges; an annular disc having anopening therethrough, and a planar portion sized for positioning betweensaid opposing flanges and for providing an extending portion extendinginto the raw water stream; means for splitting said primary additivestream into a plurality of secondary additive streams; control means formeasuring and controlling the flow rate through said secondary additivestreams; means for conveying and discharging said secondary additivestreams into said raw water stream at a plurality of respectiveinjection points; a first set of vanes fixed to said extending portionand separating the large stream into a plurality of smaller streamstherebetween, each of said respective injection points being positionedin a respective section near the centroid thereof; mixing meanscomprising a pair of propellers fixed to a shaft, means for rotatingsaid shaft, said propellers being pitched to urge fluid in the conduitin opposite directions, said shaft being positioned substantiallyperpendicular to the direction of flow of the fluid, said propellersbeing positioned adjacent opposite walls of said conduit.
 6. In a mixingstation as in claim 5 which includes a second annular disc having anopening therein, said second disc being positioned between the opposingjoint flanges which are downstream with respect to sAid mixing station,said second annular disc having projecting portions extending into thestream; a second set of vanes for dividing said stream into a pluralityof sections, said second set being fixed to said projecting portions ofsaid second disc and extending upstream with respect to said seconddisc.
 7. A method of achieving uniform and substantially instantaneousdispersion of a coagulant of a type most efficiently used bysubstantially instant dispersion, including the steps of: flowing alarge stream of liquid to be treated through a conduit; injecting acoagulant of said type, divided into several separate streams ofpredetermined flow rations, into said large stream near centroids ofcross-sectional sectors of the large stream having corresponding flowratios; and providing turbulence in the large stream for distributingthe coagulant through it, said turbulence including turbulence of thecross-sectional sectors of the large stream at positions to begin themixing of the coagulant therein substantially instantly upon injectionof the coagulant; and including a zone of vigorous turbulence with majorflow induced by propulsion means moving transversely throughout thelarge stream in a zone positioned to mix the coagulant throughout thelarge stream promptly after injection, with vigorous flow from at leastone transversely acting impeller passing through and intermixing aplurality of sectors.
 8. Apparatus for achieving uniform andsubstantially instantaneous dispersion of a coagulant including: aconduit through which flows a large stream of liquid to be treated;means for injecting a coagulant, divided into several separate streamsof predetermined flow ratios, into said large stream near centroids ofcross-sectional sectors of the large stream having corresponding flowratios; and means for providing turbulence of the cross-sectionalsectors of the large stream at positions to begin the mixing of thecoagulant therein substantially instantly upon injection of thecoagulant; said apparatus including propulsion means for providingvigorous turbulence in a zone positioned to mix the coagulant throughoutthe large stream promptly after injection by causing flow transverselythroughout the large stream, with vigorous flow from at least onetransversely acting impeller passing through and intermixing a pluralityof said sectors.
 9. A method of achieving uniform and substantiallyinstantaneous dispersion of a coagulant of a type most efficiently usedby substantially instant thorough dispersion, including the steps of:flowing a large stream of liquid to be treated through a conduit;injecting a coagulant of said type, divided into several separatestreams of predetermined flow ratios, into said large stream nearcentroids of cross-sectional sectors of the large stream havingcorresponding flow ratios; and providing turbulence in the large streamfor distributing the coagulant through it, said turbulence includingturbulence of the cross-sectional sectors of the large stream atpositions to begin the mixing of the coagulant therein substantiallyinstantly upon injection of the coagulant; and including not later thanimmediately after injection a zone of vigorous turbulence with flowmoving the coagulant at least throughout substantially the entire crosssection of each sector of the stream by movements transversely of themain direction of stream flow and transversely of each other to mix thecoagulant with good uniformity throughout the large stream promptlyafter injection.